Compact high resolution imaging apparatus

ABSTRACT

An optical coherence tomography (OCT) apparatus includes an optical source, an interferometer generating an object beam and a reference beam, a transverse scanner for scanning an object with said object beam, and a processor for generating an OCT image from an OCT signal returned by said interferometer. At least the optical source, the interferometer, and the scanner are mounted on a common translation stage displaceable towards and away from said object. A dynamic focus solution is provided when the scanner and a folded object path are placed on the translation stage.

FIELD OF THE INVENTION

The present invention relates to an optical mapping apparatus, and inparticular to an apparatus which can be used to supply images fromessentially transparent objects or tissue in general and from theanterior chamber of the eye in special.

BACKGROUND OF THE INVENTION

In the description which follows, reference is made primarily to the eyeand the anterior chamber of the eye as the object. This is to beunderstood as merely exemplary to assist in the description and not as arestriction. Where the term “eye” is used, a more general transparentand scattering object or organ may be sought instead.

Low coherence interferometry is an absolute measurement technique whichallows high resolution ranging and characterisation of optoelectroniccomponents.as presented in the papers S. A. Al-Chalabi, B. Culshaw andD. E. N. Davies, “Partially coherent sources in interferometricsensors“, First International Conference on Optical Fibre sensors, 26-28Apr. 1983, I.E.E. London, pp. 132-135, 1983, R. C. Youngquist, S. Carr,and D. E. N. Davies, “Optical coherence-domain reflectometry: A newoptical evaluation technique,” Opt. Lett. 12(3), pp. 158-160 1987 and H.H. Gilgen, R. P. Novak, R. P. Salathe, W. Hodel, P. Beaud, Submillimeteroptical reflectometry”, Lightwave Technol., Vol. 7, No. 8, pp.1225-1233, 1989.

The first application in the biomedical optics field was for themeasurement of the eye length as shown in A. F. Fercher, K. Mengedohtand W. Werner, “Eye length measurement by interferometry with partiallycoherent light”, Opt. Lett., Vol. 13, No. 3, (1988), pp. 186-189.

Adding lateral scanning to the scanning in depth, allows acquisition of3D information from the volume of biologic media. This concept, ofadding devices for lateral scanning in an interferometer, has beenpresented in papers on heterodyne scanning microscopy, such as “Opticalheterodyne scanning microscope”, published by T. Sawatari in AppliedOptics, Vol. 12, No. 11, (1973), pp. 2766-2772 and Profilometry with acoherence scanning microscope”, by B. S. Lee, T. C. Strand, published inAppl. Opt., 29, 26, 1990, 3784-3788. The later report shows a crosssection image from a semiconductor wafer proving the possibility forsubsurface imaging.

The potential of the technique for high resolution imaging of the tissueis often referred to as optical coherence tomography (OCT) as presentedin D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W.Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito and J. G.Fujimoto, ‘Optical coherence tomography’, Science 254, pp. 1178-1181,1991 and in the paper “Optical coherence tomography” by A. F. Fercher,in J. Biomed. Opt., 1(2), (1996), pp. 157-173. OCT has the potential ofachieving high depth resolution, which is determined by the coherencelength of the source. For example, optical sources, such assuperluminiscent diodes and mode-locked lasers are now available withcoherence lengths below 20 μm.

An OCT apparatus is now commercially available (e.g. from Humphrey),which produces longitudinal images only, i.e. images in the planes (x,z)or (y,z), where the z axis is perpendicular to the patient's face and xand y axes are in the plane of the patient's face. Examples of suchapparatus for longitudinal imaging are described in U.S. Pat. Nos.5,493,109, 5,537,162, 5,491,524, 5,469,261, 5,321,501 and 5,459,570(Swanson).

OCT has also been reported as being capable of providing en-face (ortransversal) images, as reported in “Coherence Imaging by Use of aNewton Rings Sampling Function” by A. Gh. Podoleanu, G. M. Dobre, D. J.Webb, D. A. Jackson, published in Opt. Lett., Vol. 21, No. 21, (1996),pp. 1789-1791, “Simultaneous En-face Imaging of Two Layers in HumanRetina” Opt. Letters, by A. Gh. Podoleanu, G. M. Dobre, D. J. Webb, D.A. Jackson, published in Opt. Lett., 1997, vol. 22, No. 13, pp. pp.1039-1041, “En-face Coherence Imaging Using Galvanometer ScannerModulation” by A. Gh. Podoleanu, G. M. Dobre, D. A. Jackson, Opt. Lett.23, pp. 147-149, 1998 and in “Transversal and Longitudinal Images fromthe Retina of the Living Eye Using Low Coherence Reflectometry”, by A.Gh. Podoleanu, Mauritius Seeger, George M. Dobre, David J. Webb, DavidA. Jackson and F. Fitzke, published in the Journal of Biomedical Optics,3(1), pp. 12-20, 1998 and in the U.S. Pat. No. 5,975,697 (Podoleanu).

As shown in the last paper mentioned above and disclosed in the lastpatent mentioned above, en-face scanning allows generation of constantdepth OCT images as well as cross section OCT images initially reportedby using longitudinal OCT.

En-face OCT imaging requires movement of at least one of the transversescanners in a 2D scanner assembly faster than the scanner performing thedepth scanning. To generate a raster looking image, the en-face OCTemploys a fast transverse scanner and a slow transverse scanner, bothoperating faster than the scanner performing the depth scanning. Inorder to adjust the reference path length, in the papers and patentsmentioned above, mirrors are used which are translated by mechanicalmeans. This is characterized by the disadvantage that the signal has tobe extracted from single mode optical fiber and reinjected back into thesame or a different single mode optical fiber. This procedure introduceslosses and requires specialized high accuracy and high mechanicalstability 3D stages for launching light into a single mode fiber. In aseries assembly line in a factory, such a configuration would requiresignificant assembly time and the final product would be expensive.

Therefore, using an all fiber reference path would be advantageous. Anall fiber configuration is disclosed in the U.S. Pat. No. 6,201,608B1.However, this disclosure employs a specialized light source whichoperates in regime of amplification for the signal returned from thetarget. Two optical paths in fiber are constructed in combination withthe specialized optical source. In this case, the depth scanning isachieved by moving a stage supporting a group of elements towards andbackwards from the object. The elements grouped on the moving stage arethe transverse scanner and the interface optics only.

Such a grouping and assembly has the added disadvantage that a fiberloop is required to connect the stage with the rest of the OCT system.When the stage moves, vibrations are induced in the fiber loop whichleads to noise. Also, the polarization of the light propagating down thefiber link may change due to the alteration in the spatial distributionof radiation within the fiber cord, which leads to reduction in thevisibility and signal to noise ratio. Such a solution requires anexpensive light source and expensive polarization maintaining fiber inorder to avoid noise generation in the fiber and changes in thepolarization due to fiber cord being shaped during the depth scanning.

Additionally, as shown in the paper by T. Sawatari mentioned above, inorder to generate an interference image in the heterodyne scanningmicroscopy, a phase or frequency modulator is required to create a bitsignal, or a carrier for the image signal. Such modulator is expensive,ads losses, reduces the efficiency in using the signal and introducesdispersion which deteriorates the depth sampling profile of the OCT.

As another disadvantage, during the stage movement, the focus positionslips away from the coherence gate position, given by the point in thevolume of the object, where the optical path difference in theinterferometer is zero. The longer the depth scanning, the larger thedifference between the focus and the coherence gate point, withdisadvantageous reduction in the signal strength.

Thus, a need exists for a better procedure of implementing the depthscanning and processing of the OCT signal. In particular, in the firstinstance, a better configuration less susceptible to noise and whichdoes not alter the polarization state would be desirable. Secondly, aprocedure having improved efficiency in using the signal and tolerant todispersion would be advantageous. Thirdly, a procedure to implementdynamic focus to maintain at least partially, the synchronism betweenthe focus and the coherence gate points during the depth scanning wouldbe desirable.

In terms of transverse resolution, this feature depends on how well thefocus is matched to the coherence position (wherein tracking of thefocusing and zero optical path difference are referred to as dynamicfocus). Dynamic focus was described in PCT patent publication No. WO92/19930, but only in principle. Possible optical configurations tosimultaneously scan the depth and the position of the focus in the depthare described in U.S. Pat. No. 4,589,773, in U.S. Pat. No. 6,057,920 andin U.S. Pat. No. 6,144,449. These solutions however, require mechanicalsynchronism of elements or adjustment of ratios of focal lenses ormovement of a bubble elastic lens respectively, with the consequencelimitation in speed.

Another method was described in the paper “An optical coherencemicroscope with enhanced resolving power in thick tissue”, by J.Schmitt, S. L. Lee and K. M. Yung, published in Optics Communications,142, (1997), pp. 203-207 where the focusing lens in the object arm wassynchronously moved with retroreflectors in the reference arm. In thisway, for a movement of the objective lens towards the tissue by x, theOPD varies by 2n²x−4, where n is an average value for the index ofrefraction of the medium. When n² is approximately 2, which happens formost of the tissue structures, then OPD is approximately zero anddynamic focus is automatically accomplished. However, the method uses amirror which redirects high power to the optical source, and it is knownthat low coherence source are prone to noise in the presence offeedback. The movement employs elements in both object and reference armwhich makes the method cumbersome to implement. Another method fordynamic focus applicable for the case when n² is approximately 2 isdisclosed in the patent WO 02/04884. This last disclosure presents asimultaneous movement of a lens and of a beam-splitter separating thereference and the object beams in the interferometer. This requiresstable mechanical fixtures, low vibrations and the method cannot beimplemented in fiber version.

The methods described above are devised especially for longitudinal OCT,where B-scan images are generated by fast scanning along the depthcoordinate with a slower scanning along a transverse coordinate. Assuch, the method needs to be fast, and operational at the depth scanningrate of, for example, a rate on the order of 100-1000 Hz.

Accordingly, the present invention provides for improvements over atleast one of the problems of the prior art as stated hereinabove, or asdescribed herein below.

SUMMARY OF THE INVENTION

In one aspect the invention provides an optical coherence tomography(OCT) apparatus comprising a low coherence optical source, aninterferometer generating an object beam and a reference beam, a scannerfor scanning an object with said object beam, and a processor forgenerating an OCT image from an OCT signal returned by saidinterferometer, a focusing element for bringing said object beam to afocus in the object, a common translation stage displaceable towards andaway from said object, and a control element controlling said focusingelement, and wherein said focusing element and said scanner are mountedon the common translation stage, and said control element maintains saidfocus in coincidence with a point in the object where the optical pathdifference between said reference beam and said object beam issubstantially zero as the common translation stage moves toward theobject.

According to another aspect, the present invention provides an opticalmapping apparatus which in a preferred embodiment, comprises an opticalradiation source which is divided into an object beam along an objectarm and a reference beam along a reference arm starting at therespective 1^(st) output and 2^(nd) output of a first optical splitter;where light from the 1^(st) output of the first optical splitter is sentto an input port 1 of a second optical splitter and the light at one ofthe corresponding output port, 2, of the second optical splitter is sentvia a focusing element towards a transverse scanning means and the port3 of the second optical splitter, where light traveling from thetransverse scanning means toward the port 2 appears, is opticallyconnected to the 1^(st) input of a third optical splitter and where the2^(nd) input of the third optical splitter receives light from the2^(nd) output of the first optical splitter via a delay line; where thesaid transverse scanning means effect 2D transverse scanning of anoptical output from the second optical splitter, over a line or apredetermined area in an object to be investigated or imaged, transversescanning means preferably consisting of a line scanner and a framescanner; interface optics for transferring an optical beam from thetransverse scanning means to the object and for transferring an opticaloutput beam reflected and scattered from the object back to transversescanning means, and therefrom to the second optical splitter; focusingmeans, which together with the interface optics means act to project afocused spot on the target or inside the volume of the objectinvestigated; optionally, when the object is the eye, a fixation lampunit, interleaved with the interface optics, for sending light towardsthe eye for guidance; balanced photodetector unit which receives lightfrom the two outputs of the third splitter; analyzing means forprocessing the signal delivered by the balanced photodetector unit;optionally, the focusing means are synchronously adjusted with themovement of the translation stage to implement dynamic focus, i.e. tomaintain the point of OPD=0 in the focus; displaying means forprocessing and generating an image created by the analysing means, whichimage is synchronised with the transverse scanning means; and where thereference path is defined as the path taken by the reference beam fromthe first splitter up to the third splitter and the object path isdefined as the path taken by the object beam from the first splitter,via the second splitter, focusing element, transverse scanning means,interface optics up to a depth inside the object to be investigated andtherefrom back via the interface optics, transverse scanning means,focusing element towards the second splitter up to the third splitterand the delay line is adjusted to match the optical length of thereference path to the length of the object path; at least a polarizationcontroller to match the orientation of the polarization in the objectand reference paths; translation stage which supports the three opticalsplitters, the polarization controller or controllers, the opticalradiation source, the focusing means, the transverse scanning means andthe interface optics, the optional fixation lamp, the optionaladjustment means of the focus, stage which can be controlled to movetowards and backwards from the object and all connections from the stageto the rest of the optical mapping apparatus are in the form of elasticelectrical cables only. In this way, profilometry of corrugated surfacesor curved surfaces such as cornea is accomplished by simultaneouslymaintaining the coherence gate in the focus.

Embodiments of the invention solve the above discussed problems andrelate to an apparatus wherein the fiber leads are not stretched duringthe depth scanning.

In another embodiment the invention provides a method and apparatus toencode the reflectivity of the backscattered signal with no increase inthe dispersion and signal loss.

In a yet another embodiment the invention provides a method andapparatus for dynamic focus.

Overall, the invention sets out a simplified, low cost configurationeasy to be assembled in series in a factory, in a very compact format.

In preferred embodiments, the second optical splitter is either a two bytwo optical splitter, or an optical circulator.

In a preferred embodiment, the three optical splitters and the delayline are implemented all in single mode fiber. In this case, in order tooptimize the signal to noise ratio, an in-fiber attenuator is used inthe form of a connector between connectors connecting the first and thethird splitter.

In a preferred embodiment, when the second optical splitter is a two bytwo optical splitter, the said first splitter is eliminated, the opticsource is connected direct to the second splitter and the reference pathis connected to one output of the second splitter.

In a preferred embodiment, a supplementary optical splitter isincorporated either between the output of the second optical splitterand the focusing means or between the second and the third opticalsplitter in order to divert some of the light backscattered by theobject towards a confocal receiver. This splitter is termed in whatfollows as a confocal optical splitter. In this case, the analyzingmeans process simultaneously two signals, one delivered by the balanceddetection unit and the other by the confocal receiver and the displayingmeans display simultaneously two images, OCT and confocal respectively.

In another embodiment, the optical source is made of two sources, afirst low coherence source to generate the OCT image and a secondoptical source, whose wavelength is advantageously chosen to maximizethe sensitivity of the photodetector used in the confocal receiver unit.

The optical radiation source is preferably a low coherence source, or asource with adjustable coherence length.

All embodiments of the present invention can operate in at least one ofthe following regimes of operation: A-scan, T, B, C-scan or 3D.

In the A-scanning regime, the transverse scanning means are fixed,deflecting the object beam to a fixed desired angular or lateralinclination, the translation stage is used to explore the depth rangeand the mapping apparatus acquires an A-scan, i.e. a one dimensionalreflectivity profiles in depth and in the embodiments of the apparatusequipped with a confocal receiver, the apparatus according to theinvention acquires simultaneously a one dimensional reflectivity profilein depth in the OCT channel and a one dimensional reflectivity profilein depth in the confocal channel.

In the T-scan regime, the transverse scanning means are used to move theobject beam angularly or laterally in a time T_(H) along a prescribedcontour, which could be a horizontal line, a vertical line, a circularpath, an elliptic path or any other open or closed path, while thetranslation stage is at rest, and a one dimensional en-face profile ofthe reflectivity versus the transverse position is obtained. In theembodiments of the apparatus equipped with a confocal receiver, theapparatus according to the invention acquires simultaneously a onedimensional en-face profile of the reflectivity versus the transverseposition in the OCT channel and a one dimensional en-face profile of thereflectivity versus the transverse position in the confocal channel.

In the B-scan regime, the said translation stage is moved in steps aftereach T-scan to cover the depth range in a number of steps whichdetermines the number of lines in the image frame, or the saidtranslation stage is moved continuously in a time T_(B)>T_(H) where thenumber of lines in the image frame is T_(B)/T_(H), generating in thisway a two dimensional map of reflectivity as a cross section through theobject in a surface containing the optic axis and the T-scan contour.

In the C-scan regime, the transverse scanning means are used to move thebeam angularly or laterally to cover a two dimensional patterndescribing different shapes of T-scans in a time T_(C) while thetranslation stage is kept fixed to generate a 2D map of reflectivity forconstant depth in the reference path of the interferometer.

In the 3D-scan regime, the translation stage is moved in small stepsafter each C-scan to cover a depth range or at a constant speed lessthan the ratio determined by dividing the depth resolution to T_(C),covering the depth range in a time T_(3D) and a number T_(3D)/T_(C) ofC-scans are stored and then used to generate a 3D image of the interiorof the object.

In order to implement a compact apparatus configuration, no externalphase modulator is employed for creating the carrier of the OCT signal.This allows the reference path to be continuous in optical fiber, forlow losses and high mechanical stability. Therefore, in the T-scan,B-scan or C-scan regimes of operation, the signal is encoded based onthe phase modulation only, created by the movement of the transversescanning means along the T-scan direction which determines the line inthe raster of the B-scan or C-scan image, movement which determinesmodulation of the interference signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 shows, in diagrammatic form, a first embodiment of the compacthigh resolution mapping apparatus providing an OCT image.

FIG. 2 shows, shows, in diagrammatic form, a second embodiment of thecompact high resolution mapping apparatus providing an OCT and aconfocal image simultaneously.

FIG. 3 shows, in diagrammatic form, a third embodiment of the compacthigh resolution mapping apparatus providing an OCT image, which insuresless deviation of the focusing gate depth from the coherence gate depth.

FIG. 4 shows, in diagrammatic form, a fourth embodiment of the compacthigh resolution mapping apparatus providing simultaneously an OCT imageand a confocal image, which insures less deviation of the focusing gatedepth from the coherence gate depth.

FIG. 5 shows, in diagrammatic form, a fifth embodiment of the compacthigh resolution mapping apparatus providing simultaneously an OCT imageand a confocal image, which insures less deviation of the focusing gatedepth from the coherence gate depth.

FIG. 6 shows, in diagrammatic form, a version of the embodiment in FIG.5 with a different position of the optical splitter of the confocalreceiver.

FIG. 7 shows, in diagrammatic form, two possible embodiments for thesecond optical splitter.

FIG. 8 shows, in diagrammatic form a different layout for the second andthird optical splitter.

FIG. 9 shows, in diagrammatic form a different layout for the second andthird optical splitter, similar to that in FIG. 8 but incorporating anoptical splitter for the confocal receiver.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various features of the present invention, as well as other objects andadvantages attendant thereto, are set forth in the following descriptionand the accompanying drawings in which like reference numerals depictlike elements.

An OCT device may involve and make use of techniques known in the artand described in GB patent(Younguist Davies) no. 8611055; U.S. Pat. No.5,459,570, U.S. Pat. No. 5,321,501, U.S. Pat. No. 5,491,524, U.S. Pat.No. 5,493,109, U.S. Pat. No. 5,365,335, U.S. Pat. No. 5,268,738, andU.S. Pat. No. 5,644,642 and U.S. Pat. No. 5,975,697 (Podoleanu), whichare herein incorporated by reference. These devices can be constructedin bulk or optical fiber, and have means for transversally scanning thetarget, means for longitudinal scanning of the reference path length,means for phase modulation, means for controlling the polarization stageas bulk or fiber polarizer controllers, and have means for compensatingfor dispersion. In embodiments of the present invention, no phasemodulator is required and because all the reference path is in fiber,the embodiments exhibit dispersion, which in accordance with theembodiments of the invention can be tolerated if proper wavelength isused, such as 1300 nm.

FIG. 1 diagrammatically shows the embodiment of a compact OCT apparatusaccording to the invention. The apparatus comprises an optical source,1, which can be either low coherence or with adjustable coherencelength, pigtailed to a single mode fiber, 2, wherefrom the power issplit in a first optical splitter, which in FIG. 1 is shown as adirectional single mode coupler, 3, into a reference beam, along thereference path 4 and an object beam, along the object path, 5. Lightinto the object path 5 is launched from the 1^(st) output of the firstsplitter and light into the reference path 4 is launched from the secondoutput of the first splitter.

In the context of the invention, a low coherence source is a broadbandsource, whose coherence length is much less than the penetration depthof the radiation used in the object studied. Examples of such sourcesinclude superluminiscent diodes, tungsten lamps, Kerr-lens mode-lockedlasers, laser diodes below threshold and diverse combinations of theabove. For instance, at the level of the technology today, the coherencelength of such sources cover the range of 0.5-500 μm. In contrast, inthe context of the invention, a high coherence source has a coherencelength much larger than the penetration depth of the radiation used inthe object studied. Examples of such sources include lasers, with acoherence length larger than 1 cm.

In the object path, a second optical splitter, 6, which in FIG. 1 isshown as an in-fiber circulator, is used to transfer light from the1^(st) output of the first optical splitter and send light, via path 7to output 8, terminated with a fiber connector at an angle, or cleavedat an angle, to minimize the fiber end reflection and in this way thenoise. From the output 8, the light is sent via free space, 9, towardsthe focusing element 10, such as a refractive or reflective opticalelement and then deflected by a 2D scanner head 11, equipped withmirrors 12 and 13 to scan transversally, via interface optics 14, anobject.

In FIG. 1 the object is either the cornea, 15 or the retina, 16, of aneye 17, in which case the beam is focused by the cornea 15 and eye lens18 onto the retina 16. The object could be any other type of tissue orindustrial object, such as powder or lenses to be tested, such objectbeing placed where cornea 15 or the retina 16 are shown in FIG. 1. Theline connecting the transverse scanning means and the object constitutesan optic axis of the apparatus, oriented along the deflected object beamin the middle of the scanning range of the transverse scanning means.

Scanner head 11 is a scanning assembly means known in the art andincludes, for example, galvanometer scanners, piezo-vibrators, polygonmirrors, resonant scanners, acousto-optic modulators, rotating orvibrating prisms etc. Combinations of scanners from the list above canbe used for the scanning pair head 11. One scanner usually works fastand the signal collected during its movement is displayed on the line inthe raster of the final image, termed as the line scanner, while theother scanner, is typically termed as frame scanner. For instance, apolygon mirror can be used as the line scanner and a galvanometerscanner can be used as the frame scanner. The scanner head 11 is underthe control of triangle, saw-tooth or DC voltages produced by agenerator 19.

The scanning head 11 can be divided in two parts, namely the linescanner and the frame scanner, separated by optical elements like lensesand/or mirrors in configurations known in the art of scanning laserophthalmoscopes (SLO) aand of confocal microscopy or general rasterscanning systems, in which case the scanner head 11 and interface optics14 are interleaved to each other, in one block, and only for convenienceare they represented here separately. The scanner mirrors, 12 and 13,which refer to either galvanometer scanners or polygon mirrors have highreflectivity at the wavelength used, or if acousto-optic modulators areused, their transmission at the wavelength used is high. By means knownin the art, the two scanners have orthogonal axes or scan the ray inperpendicular planes, producing a raster in the plane (X,Y), orientedperpendicular on the optic axis of the system. Circular scan, (ρ,θ) ofthe ray can also be obtained by sinusoidally scanning the ray using thetwo scanners in orthogonal directions at the same frequency with a phasedifference of π/2, where α is determined by the amplitude of the angulardeviation, measured in a plane perpendicular on the optic axis from thepoint hit by the ray when the scanners are not driven, and 74 is a polarangle in this same plane.

Light returned from the object, via the interface optics 14, and thenvia the scanning head 11, is launched via the focusing elements 10 backinto the second optical splitter 6, i.e. into the same port fiber, 7 ofthe circulator, 6, where the light originated from. The circulatorroutes the signal to the fiber output 20, which takes the signal to afirst input of a third optical splitter 21, which in FIG. 1 is shown asa single mode directional coupler. The second input of the opticalsplitter 21 receives light from the reference path, 4, via a fiber delayline 4′. The object signal interferes with the reference signal when theoptical path difference (OPD) between the reference path length and theobject path length is less than the coherence length of the source 1.This explains the selection in depth of the OCT. The reference pathstarts at the optical splitter 3 and ends at the optical splitter 21,and is made of fiber 4 and delay line 4′. The object path starts fromthe optical splitter 3 and again ends on the optical splitter 21, madeout of fiber 5, circulator 6, fiber 7, fiber connector 8, free spacepath 9, focusing element 10, scanner head 11, interface optics 14 up tothe object and back to the fiber 7. Points along the object beam in thevolume of the object will contribute to the signal only from within thecoherence length of the source in the volume of the object. Thedisclosure in FIG. 1 has the advantage that the reference beam is all infiber and no losses or vibration induced noise are incurred due topassing the light from fiber to free air and back, to allow for theadjustment of the reference path length. The OPD is adjusted instead onthe expense of the object path length only. Such a configurationrequires less assembly time, essential in series production. As fiberlength compensates for the path in air in FIG. 1, dispersion may existwhich may enlarge the depth sampling profile of the apparatus. However,it is known that single mode fiber at 1300 exhibits little dispersion.Because there is no loss in the reference arm, excess photon noise maybe large, and in order to maximize the signal to noise ratio,attenuation of reference path is required. In this case, suchattenuation can be obtained by introducing an adaptor between FC/APCconnectors, where the mating of the two connectors in the reference arm,such as the two tilted connectors bringing fiber from the first or thesecond splitter towards the connector of the thirs splitter, are set atdifferent angles in between. In this way, by changing the adaptor, whichhas different slits for the two FC/APC connectors, different attenuationcan be introduced, at a set value dependent on the relative rotationorientation of the two FC/APC or FC/ST or other types of connectorsknown in the art.

To maximize the interference signal, polarization of light in the twoarms of the interferometer needs to be the same. Therefore, at least apolarization controller 29 in one of the object path or reference pathis required.

The optical splitter 21 is terminated on two photodetectors 22, 23 of abalanced photoreceiver unit 24. Preferably the splitter 21 needs to bean even 50/50 splitter for the whole band of wavelengths used, in orderto achieve suitable reduction of the intensity noise and excess photonnoise characteristic for low coherence sources. The photodetected signalobtained at the electrical connector output, 25, of the unit 24 is sentto the processing block 26 to provide strength proportional to thereflectivity, or the log version of the reflectivity, and then displayedand recorded by means of a suitable display device 27, such as a framegrabber, a storage oscilloscope or a suitable printer. The device 27 isunder the control of computer 28. The block 26 contains a band passfilter followed by a rectifier and a low pass filter.

The filter is adjusted on two different functions depending on theregime of operation of the apparatus, as described below.

In the T-scan regime, the transverse scanning means are used to move theobject beam angularly or laterally in a time T_(H) along a prescribedcontour, which could be a horizontal line, a vertical line, a circularpath, an elliptic path or any other open or closed path, while thetranslation stage is at rest, and a one dimensional en-face profile ofthe reflectivity versus the transverse position is obtained.

In the B-scan regime, the said translation stage is moved in steps aftereach T-scan to cover the depth range in a number of steps whichdetermines the number of lines in the image frame, or the saidtranslation stage is moved continuously in a time T_(B)>T_(H) where thenumber of lines in the image frame is T_(B)/T_(H), generating in thisway a two dimensional map of reflectivity as a cross section through theobject in a surface containing the optic axis and the T-scan contour.

In the C-scan regime, the transverse scanning means are used to move thebeam angularly or laterally to cover a two dimensional patterndescribing different shapes of T-scans in a time T_(C) while thetranslation stage is kept fixed to generate a map of reflectivity forconstant depth in the reference path of the interferometer.

In the 3D-scan regime, the translation stage is moved in small stepsafter each C-scan to cover a depth range or at a constant speed lessthan the ratio determined by dividing the depth resolution to T_(C),covering the depth range in a time T_(3D) and a number T_(3D)/T_(C) ofC-scans are stored and then used to generate a 3D image of the interiorof the object.

In order to implement a compact apparatus configuration, no externalphase modulator is employed for creating the carrier of the OCT signal.This has in fact allowed the reference path in FIG. 1 to be continuousfor low losses and less vibration induced noise. Therefore, in theT-scan, B-scan or C-scan regimes of operation, the signal is encodedbased on the phase modulation only, created by the movement of thetransverse scanning means along the T-scan direction which determinesthe line in the raster of the B-scan or C-scan image, movement whichdetermines modulation of the interference signal. The band pass filterin the block 26 is tuned on this modulation signal having a sufficientlarge band to insure sufficient transverse resolution in the T, B orC-scan image displayed by the displaying means. The low pass filterafter the rectifier has also a similar band and both bands, of the bandpass filter and of the low pass filter in the block 26 are adjustedexperimentally as a trade-off between smearing the transverse pixel sizein the image and the noise. Such an operation was disclosed in the U.S.Pat. No. 5,975,697 and the PCT patent WO00142735A1. Also, as explainedin these patents, it is possible to increase the frequency of modulationof the interference signal generated by moving the object beam angularlyor laterally along the T-scan contour. For instance, when using galvo orresonant scanners, by moving the incident beam on the scanning mirroraway from the center of rotation, higher frequencies are generated whenscanning the object. This is advantageous in order to better attenuatethe low frequency noise components.

In the A-scanning regime, the transverse scanning means are fixed,deflecting the object beam to a fixed desired angular or lateralinclination, the translation stage is used to explore the depth rangeand the mapping apparatus acquires A-scans, i.e. one dimensionalreflectivity profiles in depth. In opposition to the regimes above, thefilter in the block 26 is tuned on the Doppler frequency f_(D)=2v/λ,where v is the translation stage velocity and λ the central wavelengthof the optical source used.

For example, a T-scan covering N_(T)=250 pixels requires a minimumbandwidth of 2N_(T)/T, which for T_(H)=1 ms leads to 500 kHz. Theinterference signal is modulated in intensity by the object beamscanning the transverse pixels. The band pass filter has to accommodatelike in any imaging problem a sufficient large band to display thepixels with little lateral smear. Therefore, a possible implementationof the band pass filter is as a combination of a low pass filter with acut-off 2N_(T)/T_(H)=500 kHz and a high pass filter with a cut-off of 50kHz to eliminate the harmonics of vibration noise and the 1/f noise. Ina typical B-scan imaging or C-scan imaging, T_(B) is approximatelyT_(C)=0.5 s. To cover a 1 mm in depth in the B-scan regime, the stage ismoved at 2 mm/s.

The resultant image can be displayed in linear or logarithmic scale ongrey or false colour coded format. The depth in the OCT channel isscanned by moving the stage 31 back and forward towards the object 15 or16, changing the optical path in the object path.

All the elements within the dashed contour 40 belong to the coreinterferometer. All the elements within the block 30 are moved togetherby the stage 31. Optionally, the focusing adjustment element, 10, may becontrolled from the computer, 28, via a translation stage 36, tomaintain the focus in the object in synchronism with the position wherethe optical path difference is zero.

Optionally, when the object is the eye, a fixation lamp unit, 46,interleaved with the interface optics 14, is used for sending lighttowards the eye for guidance of the patient. Such a fixation lamp uses abeamsplitter or a dychroic filter by means known in the art toconveniently send light from a visible source to the eye, and move thissource laterally by mechanical means, or by using a liquid crystal or a2D LED array to move a spot, a cross or a star or a shaped luminouspoint laterally by electric means. The fixation lamp is powered by apower supply 47.

All optics connections are moved together which minimizes the vibrationinduced noise and polarization induced changes due to moving fiberleads. Electrical connections, similar to 25 are provided, 32, for thepower supply 33 of the optical source, 34, for the signals driving thescanning head 11, and 35, for the signal driving the focusing adjustment36 and 48 for the fixation lamp 46. Electrical loops 37, 38, 39, 41 and49 are provided to allow for the free movement of the stage 31.

Placing all OCT elements on the moving stage, apart from the electronicprocessing blocks, presents the advantage that it eliminates all effectsrelated to the movement of the fiber leads in previous art. The presentdisclosure reduces or eliminates polarisation effects, intensityvariations, etc. with all optical signals processed on the moving stage31. This has the advantage of profilometry of curves surfaces, where thecoherence gate and the focus are in synchronism during the depthscanning.

The lens 10 and interface optics 14 can be implemented using reflectiveelements or combination of refractive and reflective elements. Thesignal driving the transverse scanner may have other forms differentfrom triangle or sinusoid and the only essential feature for thisoperation is that the signal is periodic.

It will also be appreciated that instead of using the pulses 19′generated by the driver 19 it is possible to drive the display device 27with a signal, 11′, proportional with the position of the transversescanners in the block 11 as described in a co-pending patent applicationentitled “Optical Mapping Apparatus with Adjustable Depth Resolution andMultiple Functionality”, by A. Gh. Podoleanu, J. A. Rogers, G. Dobre, R.Cucu, D. A. Jackson, filed in the US Patent Office, Ser. No. 10/259671,on Sep. 9, 2002.

The same principle could be applied for the depth direction, where thetranslation stage is driven by triangle signals or controlled by the PC28 and the display means 27 is controlled by a position sensing elementinside the translation stage, which delivers a position sensing signal,31′.

The embodiment in FIG. 1 shows all optical splitters and delays infiber. However, each splitter can also be implemented in bulk. So, thesplitters 3 and 21, shown as directional couplers in FIG. 1 could beeasily replaced by plate or cube beam-splitters. Similarly, thecirculator 6 could also be replaced by a plate or a bulk beam-splitter,as shown in FIG. 7 b. A circulator function could also be implemented inbulk as shown in FIG. 7 a, using a polarization beam-splitter 68followed in the path 7 by a quarter wave plate 67 according toprinciples known by those skilled in the art. If light from the firstoutput of the first optical splitter is linearly polarized by thepolarizer 66, then light is transmitted to one output of the splitter 68only. Light is circularly polarized by the quarter wave plate 67oriented at 45° with respect to the direction of the linear polarisationof the light immediately after 68. From a mirror, light is returned as acircularly polarized light of opposite handedness and after 67 islinearly polarized along a rectangular direction to that of the incidentlight to 68 and therefore light will now appear at the other input ofthe splitter 68, i.e. all light will be transferred to path 20.

Also, the delay 4′ can be implemented by using folded free space pathsknown for those skilled in the art and all the fiber connections, 2, 4,5 and 20 could be free space paths.

A problem with using OCT imaging systems is that due to the low value ofthe coherence length, finding the position where the OPD=0 may bedifficult. The placement of the object where OPD=0 is found by movingthe object along the optic axis to and from the translation stage 30 andwatching for the image on the screen of the PC 28. If the object ismoved too fast, the position of OPD=0 may be missed. As an additionaldisadvantage, if the object is the eye, this procedure cannot beemployed by the user on her or his own. Two persons are required. Theinvention provides for a solution in this respect, where an AF amplifierblock 55 sends the rectified OCT signal towards a loudspeaker. In thisway, self-imaging is possible, procedure useful in the adjustment of theapparatus, where adjustment of the eye position can be executed byfollowing the sound emitted by the loudspeaker of 55, with no need of asecond person.

Another embodiment of the present invention is shown in FIG. 2. Inaddition to the elements in the embodiment presented in FIG. 1, aconfocal optical splitter, 61 is placed in the object path 9 leading tothe focusing element 10. This diverts some of the light returned fromthe object 15 or 16 to a confocal receiver, 62. A confocal receiver isimplemented using a pinhole and a high gain photodetector amplifier,equipped with an avalanche photodiode or a photomultiplier, by meansknown in the art and described in the copending application “Opticalmapping apparatus with adjustable depth resolution and multiplefunctionality”, by A. Gh. Podoleanu, J. A. Rogers, G. Dobre, R. Cucu, D.A. Jackson, U.S. application Ser. Nos. 10/259671, 30 Sep. 2002(International PCT application: PCT/CA03/00993.). In the embodiment inFIG. 2 the splitter 61 and confocal receiver 62 are mounted on the samestage 30 as the other optical elements and moved together. A flexiblecoaxial cable, via connector 63 and loop 64 delivers the signal from theoutput of the confocal receiver channel to the displaying means 27,which could be implemented for example by a two input digital framegrabber under the control of the PC control 28. Preferably, the splitter61 is a plate beam-splitter, sufficiently thick to avoid multiplereflections being returned to the fiber end 8, as explained in theco-pending application “Optical Mapping Apparatus with Optimised OCTConfiguration”, by Adrian Podoleanu, George Dobre, Radu Cucu, JohnRogers, David Jackson, USA Application, May 2003, number unknown. Thissplitter has an optimum splitting ratio as explained in the U.S. Pat.No. 5,975,697 to insure similar signal to noise ratios in the twochannels, OCT and confocal. The splitting ratio could be foundexperimentally as 1 to 18% power diverted to the confocal receiver 62from the power returned from the object 15 or 16.

The confocal splitter 61 is used in transmission by the OCT signal andreflection by the confocal channel in FIG. 2, however it should beobvious for those skilled in the art and equally, the optical splitter61 can be used in transmission by the confocal signal and in reflectionby the OCT signal without departing from the scope of the invention.

The confocal optical splitter 61 can also be mounted between the secondoptical splitter 6 and the third optical splitter 21 as shown in FIG. 3.The alike elements carry the same numbers as in the embodiments in FIGS.1 and 2. If the confocal optical splitter 61 is implemented in fiber, asshown in FIG. 3 by a single mode directional coupler, then the otherinput 45 is terminated with fiber cleaved at an angle or with an angledcleaved connector such as those known in the art, FC/APC or equivalent,in order to avoid multiple reflections among different fiber ends of theoptical splitters used in the core interferometer 40. The advantage ofplacing the confocal splitter 61 between the second and the thirdoptical splitter is in less loss of object power sent to the object 15or 16.

Two optical sources, 1 and 1′ launch light into the input 2 of the firstoptical splitter 3 via a fifth optical splitter 71. The sources 1 and 1′should have substantially different wavelengths in those cases where thewavelength of the source 1 to be used for the OCT is such long, as thesensitivity of Silicon avalanche photodiodes or photomultipliers to beused in the confocal receiver 62 is too low. For instance, when thewavelength of the source 1 is longer than 1000 nm, then a source 1′which could be a low coherence source or a highly coherent source suchas a laser, emitting on a wavelength shorter than 900 nm could beemployed, wavelength which could be advantageously processed by low costSilicon avalanche photodiodes or photomultiplier tubes. When thewavelengths of the sources 1 and 1′ are sufficiently different, then theconfocal optical splitter 61 and the fifth optical splitter 71 could useWDM couplers or dychroic filters if implemented in bulk, means known inthe art. This will minimize the losses at the OCT wavelength of thesource 1 and at the confocal receiver wavelength of the source 1′.

It is obvious that the utilization of two sources 1 and 1′ and of WDM ordychroic filters as described here in connection to the embodiment inFIG. 3 is equally applicable for the embodiment in FIG. 2 where theconfocal optical splitter was placed between the second optical splitter6 and the transverse scanning block 11.

The technique of using different wavelengths for the two channels, OCTand confocal was disclosed in the copending application “Optical mappingapparatus with adjustable depth resolution and multiple functionality”,by A. Gh. Podoleanu, J. A. Rogers, G. Dobre

R. Cucu, D. A. Jackson, U.S. application Ser. No. 10/259671, 30 Sep.2002 (International PCT application: PCT/CA03/00993.)

Another embodiment of the present invention is shown in FIG. 4. Thealike elements carry the same numbers as in the previous embodiments.The circulator output along the path 7, shown in fiber in FIG. 4, isterminated with a fiber end connector cleaved at an angle, 8. whichlaunches light towards the mirrors 41 and 42 which redirect the light inthe opposite direction towards the scanning head 11. In this embodiment,the support 30 moved by the translation stage 31 contains the mirrors41, 42, the scanning head 11 and the interface optics 14. For a movementof the stage 31 by x, towards the object 15 or 16, the focus point movesinside the object by nx and the optic path changes by n²x. Due to theround trip path, the object path increases by 2n²x. The optic pathdifference changes by 2n²x−4x. This represents an insignificant value ifn is approximately 1.41. With this assumption, the movement of thecoherence gate is approximately synchronous with the movement of thefocus gate in tissue. In comparison to the implementation described inthe Schmitt's paper mentioned above, the embodiment in FIG. 4 is simpleras it alters object path only and the reference path can be routedseparately and away from the moving elements. This novel dynamic focusprocedure is consistent with the aim of this disclosure for a compactsystem, easy to assemble, as here, only the object path is folded. Theimplementation in FIG. 4 allows a continuous fiber connection in thereference path with advantages in the assembly time of the apparatus.Evidently, no fiber optic lead is involved in the moving parts which isadvantageous in terms of noise or polarization induced noise. Ascommented in relation to the embodiment in FIG. 1, the coreinterferometer enclosed within the dashed area 40 can be equallyimplemented in free space or hybrid, as a combination of single modecouplers or bulk beam-splitters with the second optical splitter 6implemented in bulk or in fiber, either as a simple splitter as shown inFIG. 7 b or as a bulk circulator as shown in FIG. 7 a.

This embodiment has the advantage that for the same movement x of thestage 31, the OPD changes by 4x instead of 2x in FIGS. 1-3.

A version of the embodiment in FIG. 4 is shown in FIG. 5. In addition tothe elements in the embodiment presented in FIG. 4, a confocal opticalsplitter, 61 is placed in the object path 9 leading to the 2D transversescanner 11. This diverts some of the light returned from the object 15or 16 to a confocal receiver, 62. A confocal receiver is implementedusing a pinhole and a high gain photodetector amplifier, equipped withan avalanche photodiode or a photomultiplier, by means known in the artand described in the copending application “Optical mapping apparatuswith adjustable depth resolution and multiple functionality”, by A. Gh.Podoleanu, J. A. Rogers, G. Dobre, R. Cucu, D. A. Jackson, U.S.application Ser. Nos. 10/259671, Sep. 30, 2002 (International PCTapplication: PCT/CA03/00993.)). The splitter 61 and confocal receiver 62could be mounted on the same stage 30 moved by the translation stage 31,anywhere between the mirrors 41 and 42, or before mirror 41, or aftermirror 42, or fixed between the focusing element 10 and the movingmirror 42. If placed on the stage, then a flexible coaxial cable, viaconnector 63 and loop 64 should be used to delivers the signal from theoutput of the confocal receiver 62 to the displaying means 27, asexplained in connection with the embodiment in FIG. 2. Preferably, theconfocal optical splitter and confocal receiver are fixed, placedoutside the stage 30, as shown in FIG. 5, in which case a coaxial cable62′ connects the confocal receiver 62 to the dual input displaying means27, which could be implemented for example by a two input digital framegrabber under the control of the PC 28.

Preferably, the splitter 61 is a plate beam-splitter, sufficiently thickto avoid multiple reflections being returned to the fiber end 8, asexplained in the co-pending application “Optical Mapping Apparatus withOptimised OCT Configuration”, by Adrian Podoleanu, George Dobre, RaduCucu, John Rogers, David Jackson, USA Application, May 2003, numberunknown. This splitter has an optimum splitting ratio as explained inthe U.S. Pat. No. 5,975,697 to insure similar signal to noise ratios inthe two channels, OCT and confocal. The splitting ratio could be foundexperimentally as 1 to 18% power diverted to the confocal receiver 62from the power returned from the object 15 or 16.

The confocal optical splitter 61 can also be mounted between the secondoptical splitter 6 and the third optical splitter 21 as shown in FIG. 6.The alike elements carry the same numbers as in the embodiment in FIGS.4 and 5. If the confocal optical splitter 61 is implemented in fiber, asshown in FIG. 6 by a single mode directional coupler, then the otherinput 45 is terminated with fiber cleaved at an angle or with an angledcleaved connector such as those known in the art, FC/APC or equivalent,in order to avoid multiple reflections among different fiber ends of theoptical splitters used in the core interferometer 40. The advantage ofplacing the confocal splitter 61 between the second and the thirdoptical splitter is in less loss of object power sent to the object 15or 16.

Optionally, as described in connection to the embodiment in FIG. 3, twosources 1 and 1′ of different wavelengths can be used to launch lightinto the input 2 of the first optical splitter 3 via a fifth opticalsplitter 71. The sources 1 and 1′ should have substantially differentwavelengths in those cases where the wavelength of the source 1 to beused for the OCT is such long, as the sensitivity of Silicon avalanchephotodiodes or photomultipliers to be used in the confocal receiver 62is to low. For instance, when the wavelength of the source 1 is longerthan 1000 nm, then a source 1′ which could be a low coherence source ora highly coherent source such as a laser, emitting on a wavelengthshorter than 900 nm could be employed, wavelength which could beadvantageously processed by low cost Silicon avalanche photodiodes orphotomultiplier tubes. When the wavelengths of the sources 1 and 1′ aresufficiently different, then the confocal optical splitter 61 and thefifth optical splitter 71 could use WDM couplers or dychroic filters ifimplemented in bulk, means known in the art. This will minimize thelosses at the OCT wavelength of the source 1 and at the confocalreceiver wavelength of the source 1′.

The technique of using different wavelengths for the two channels, OCTand confocal was disclosed in the copending application “Optical mappingapparatus with adjustable depth resolution and multiple functionality”,by A. Gh. Podoleanu, J. A. Rogers, G. Dobre R. Cucu, D. A. Jackson, U.S.application Ser. Nos. 10/259671, Sep. 30, 2002 (International PCTapplication: PCT/CA03/00993.)

When the second optical splitter 6 is implemented as a two by twosplitter, as shown in FIG. 7 b, an alternative interferometer core 30can be devised as shown in FIGS. 8 and 9.

FIG. 7 b shows the utilization of a two by two splitter in theembodiments disclosed in FIGS. 1 to 6, where only three ports are used,connected to the paths 5, 7 (towards to object) and towards path 20. Thefourth is terminated on an FC/APC connector, 8′, or with fiber cleavedat an angle to avoid stray reflections and keep noise low. In FIGS. 8and 9, all four ports of a two by two splitter are used. FIG. 8discloses such an embodiment where light from the optical source 1 isinjected direct into the second splitter 6. In opposition to the use ofa two by two splitter as the second splitter 6 in the embodiments inFIGS. 1 to 6, here all four ports are used. Similar to the previousembodiments, light retroreflected from the object is sent via path 20towards the third optical splitter 21. Here the fourth port, unused inprevious embodiments is employed to send light from the optical source 1towards the reference path 4. The splitter 6 has a splitting ratio tooptimize the signal to noise ratio. Such an analysis has been presentedin our co-pending application “Optical Mapping Apparatus with OptimisedOCT Configuration”, by Adrian Podoleanu, George Dobre, Radu Cucu, JohnRogers, David Jackson, USA Application, May 2003, number unknown.

The embodiment in FIG. 8 of the core interferometer 40 could equally beused in any of the embodiments disclosed in FIGS. 1, 2, 4 and 5.

The embodiment in FIG. 9 of the core interferometer 40 is a version ofthe embodiment in FIG. 8 where the confocal optical splitter 61 isincorporated between the 2^(nd) splitter 6 and the third splitter 21, todivert light towards the confocal receiver. This embodiment couldequally be used in any of the embodiments disclosed in FIGS. 3 and 6.

Thus, it is apparent that there has been provided, in accordance withthe present invention, an optical mapping apparatus which fullysatisfies the means, objects, and advantages set forth hereinbefore.Therefore, having described specific embodiments of the presentinvention, it will be understood that alternatives, modifications andvariations thereof may be suggested to those skilled in the art, andthat it is intended that the present specification embrace all suchalternatives, modifications and variations as fall within the scope ofthe appended claims.

1. An optical coherence tomography (OCT) apparatus comprising a lowcoherence optical source, an interferometer generating an object beamand a reference beam, a scanner for scanning an object with said objectbeam, a processor for generating an OCT image from an OCT signalreturned by said interferometer, a focusing element for bringing saidobject beam to a focus in the object, a common translation stagedisplaceable towards and away from said object, and a control elementcontrolling said focusing element, and wherein said focusing element andsaid scanner are mounted on the common translation stage, and saidcontrol element maintains said focus in coincidence with a point in theobject where the optical path difference between said reference beam andsaid object beam is substantially zero as the common translation stagemoves toward the object.
 2. The optical coherence tomography apparatusof claim 1, further comprising a confocal imaging system for generatinga second image of said object, and wherein said confocal imaging systemcomprises a confocal splitter and confocal receiver, each of which ismounted on said common translation stage.
 3. The optical coherencetomography apparatus of claim 2, wherein said second image issimultaneously produced and displayed with the said OCT image and ispixel to pixel correspondent.
 4. The optical coherence tomographyapparatus of claim 2, wherein said interferometer comprises an outputport for sending light returned from the object to said confocalreceiver.
 5. The optical coherence tomography apparatus of claim 4,further comprising a splitter within the object path of saidinterferometer for directing a portion of the light returned from theobject to said confocal receiver via said output port.
 6. The opticalcoherence tomography apparatus of claim 2, wherein light from an outputobject beam port of said interferometer is sent to a first input of saidconfocal splitter and then via a focusing element towards the saidtransverse scanner; and light returned from the object is directed to asecond input of the confocal splitter whereby one portion of saidreturned light is sent to the confocal receiver and another portion ofsaid returned light is returned to said interferometer.
 7. The opticalcoherence tomography apparatus of claim 6, wherein said scanner consistsof a line scanner and a frame scanner.
 8. The optical coherencetomography apparatus of claim 2, wherein said optical radiation sourceis synthesized from two sources, a first source of low coherence, with acoherence length less than 1 mm, and a second source, which could beeither of low or high coherence such as a laser, where the secondoptical source has a substantially different central wavelength than thewavelength of the first optical source, chosen in a range where thephotodetector in the said confocal receiver has maximum sensitivity andwhere the two sources are coupled to the input of the said coreinterferometer via an optical splitter, and where this optical splitterand the confocal splitter could be implemented using a free space bulksplitter or a fiber directional coupler or a WDM coupler.
 9. The opticalcoherence tomography apparatus of claim 8, wherein the centralwavelength of the said second optical source is in the range 400-1000nm.
 10. The optical coherence tomography apparatus of claim 1, whereinsaid focusing element is displaceably mounted on said common translationstage, and said control element displaces said focusing element tomaintain said focus in coincidence with said point.
 11. The opticalcoherence tomography apparatus of claim 1, wherein the optical pathsbetween components on said translation stage are exclusively in opticalfiber, whereby said reference beam is exclusively in optical fiber andas much as possible of said object beam is in fiber.
 12. The opticalcoherence tomography apparatus of claim 11, wherein the centralwavelength of the said optical source employed is close to the minimumdispersion of the optical fiber.
 13. The optical coherence tomographyapparatus of claim 12, wherein the wavelength of the optical source isin the 1300 nm band.
 14. The optical coherence tomography apparatus ofclaim 1, further comprising an audio device to provide an audioindication of the OCT signal.
 15. The optical coherence tomographyapparatus of claim 1, wherein in said interferometer light from saidreference beam and said object beam is recombined in a splitterproviding a pair of output ports, and further comprising a balanceddetector mounted on said common translation stage for receiving OCTsignals from said pair of output ports.
 16. The optical coherencetomography apparatus of claim 1, wherein the components of saidapparatus that are mounted on said common translation stage areconnected to the remainder of said apparatus only by flexible electriccables.
 17. The optical coherence tomography apparatus of claim 1,wherein said transverse scanner is configured to effect two-dimensionaltransverse scanning of the object beam over a line or a predeterminedarea in the object.
 18. The optical coherence tomography apparatus ofclaim 1, further comprising a fixation lamp unit, interleaved withinterface optics, for sending light towards the object for guidance. 19.The optical coherence tomography apparatus of claim 1, wherein the saidtransverse scanner and said common translation stage support interfaceoptics and reflectors for a 180° folded object path, and wherein saidreflectors receive an optical output beam from an optical splitter via alauncher which is placed on the same side of the translation stage asthe abject in such a way that when the stage moves, the variation of theoptical path from the launcher to the stage substantially equals thevariation of the path measured from the interface optics on the stage upto the scattering point where signal is collected from the volume of theobject.
 20. The optical coherence tomography apparatus of claim 19,further comprising a confocal splitter in the object path leading tosaid launcher for directing a portion of the light returned from theobject to a confocal receiver.
 21. The optical coherence tomographyapparatus of claim 19, further comprising a splitter in the path of thereturned object beam in said interferometer for directing a portion ofthe light returned from the object to a confocal receiver.
 22. Theoptical coherence tomography apparatus of claim 19, which operates in atleast one of the following regimes of operation: T, B, C-scan or 3D; andwherein: where in the T-scan regime, the transverse scanning means areused to move the object beam angularly or laterally in a time T_(H)along a prescribed contour, which could be a horizontal line, a verticalline, a circular path, an elliptic path or any other open or closedpath, while the translation stage is at rest, and a one dimensionalen-face profile of the reflectivity versus the transverse position isobtained, and the mapping apparatus acquires simultaneously a onedimensional en-face profile of the reflectivity versus the transverseposition in the OCT channel and a one dimensional en-face profile of thereflectivity versus the transverse position in the confocal channel; inthe B-scan regime, the said translation stage is moved in steps aftereach T-scan to cover the depth range in a number of steps whichdetermines the number of lines in the image frame, or the saidtranslation stage is moved continuously in a time T_(B)>T_(H) where thenumber of lines in the image frame is T_(B)/T_(H), generating in thisway a two dimensional map of reflectivity as a cross section through theobject in a surface containing the optic axis and the T-scan contour; inthe C-scan regime, the transverse scanning means are used to move thebeam angularly or laterally to cover a two dimensional patterndescribing different shapes of T-scans in a time T_(C) while thetranslation stage is kept fixed to generate a map of reflectivity forconstant depth in the reference path of the interferometer; and in the3D-scan regime, the translation stage is moved in small steps after eachC-scan to cover a depth range or at a constant speed less than the ratiodetermined by dividing the depth resolution to T_(c), covering the depthrange in a time T_(3D) and a number T_(3D)/T_(C) of C-scans are storedand then used to generate a 3D image of the interior of the object. 23.The optical coherence tomography apparatus of claim 22, whereinirrespective of the regime of operation, T-scan, B-scan or C-scan, thesignal is encoded based on a phase modulation only, said phasemodulation created by the movement of the transverse scanning meansalong the T-scan direction which determines the line in the raster ofthe B-scan or C-scan image, movement which determines modulation of theinterference signal and where the photodetected signal after thebalanced detection unit passes through a band pass filter tuned on thismodulation signal having a sufficient large band to insure sufficienttransverse resolution in the T, B or C-scan image displayed by thedisplaying means.
 24. The optical coherence tomography apparatus ofclaim 22, wherein, irrespective of the regime of operation, T-scan,B-scan or C-scan, the signal in the OCT channel is encoded based on aphase modulation only, said phase modulation created by the movement ofthe transverse scanning means along the T-scan direction whichdetermines the line in the raster of the B-scan or C-scan image,movement which determines modulation of the interference signal andwhere the photodetected signal after the balanced detection unit passesthrough a band pass filter tuned on this modulation signal having asufficient large band to insure sufficient transverse resolution in theT, B or C-scan image displayed by the displaying means; the signal inthe confocal channel is processed via a DC amplifier and via a low passfilter with a sufficient cut-off to allow better transverse definitionin the image displayed by the displaying means.
 25. The opticalcoherence tomography apparatus of claim 24, wherein the frequency ofmodulation of the interference signal due to moving the object beamangularly or laterally along the T-scan contour is increased by movingthe incident beam on the scanning mirror away from the center ofrotation.
 26. The optical coherence tomography apparatus of claim 22,where the signal delivered by the balanced photodetector unit isprocessed via a band-pass filter tuned on the Doppler frequency 2v/λ,with λ the central wavelength of the said source and v the velocity ofmoving the said translation stage; the signal in the confocal channel isprocessed via a DC amplifier and via a low pass filter with a sufficientcut-off to allow better transverse definition in the image displayed bythe displaying means.
 27. The optical coherence tomography apparatus ofclaim 22, where the signal delivered by the balanced photodetector unitis processed via a band-pass filter tuned on the Doppler frequency 4v/λ,with λ the central wavelength of the said source and v the velocity ofmoving the said translation stage; the signal in the confocal channel isprocessed via a DC amplifier and via a low pass filter with a sufficientcut-off to allow better transverse definition in the image displayed bythe displaying means.
 28. The optical coherence tomography apparatus ofclaim 1, wherein: said interferometer has a core interferometer whichhas an input port for radiation source, an output object beam port forthe object beam and two output interference ports and includes means fordividing the input beam along an object arm and a reference beam along areference arm each starting at the respective first output and secondoutput of a first optical splitter; light from the first output of thefirst optical splitter is sent to a first input port of a second opticalsplitter and the light at one of the corresponding output ports of thesecond optical splitter is sent towards the said output object beam portof the interferometer and the port of the second optical splitter,wherein light traveling from the said output object beam port of theinterferometer is optically connected to the first input of a thirdoptical splitter and where the second input of the third opticalsplitter receives light from the second output of the first opticalsplitter via a delay line and where the outputs of the third opticalsplitter provide signals to the two said output interference ports ofthe interferometer; the reference path is defined as the path taken bythe reference beam from the first optical splitter via the delay line upto the third splitter; the delay line is adjusted to match the opticallength of the reference path to the length of the object path; and apolarization controller is provided to match the orientation of thepolarization in the object and reference paths.
 29. The opticalcoherence tomography apparatus of claim 28, wherein said focusingelement is synchronously adjusted with the movement of the translationstage.
 30. The optical coherence tomography apparatus of claim 1,wherein said focusing element is synchronously adjusted with themovement of the translation.
 31. The optical coherence tomographyapparatus of claim 1, wherein: said interferometer has a coreinterferometer which has an input port for radiation source, an outputobject beam port for the object beam and two output interference portsand includes a means for dividing an input beam along an object arm anda reference beam along a reference arm starting at the respective firstoutput and a second output of a second optical splitter, where lightfrom the first output of the second optical splitter is sent to the saidoutput object beam port for the object beam of the core interferometerand the second output of the second optical splitter is opticallyconnected via a delay line to a first input of a third optical splitterwhose outputs sends light towards the said two output interference portsof the interferometer and where the second input of the second opticalsplitter is optically connected to the 1^(st) input of the third opticalsplitter; the reference path is defined as the path taken by thereference beam from the second optical splitter via the delay line up tothe third optical splitter; the delay line is adjusted to match theoptical length of the reference path to the length of the object path;and a polarization controller is provided to match the orientation ofthe polarization in the object and reference paths.
 32. The opticalcoherence tomography apparatus of claim 1, wherein: said interferometerhas a core interferometer which has an input port for the radiationsource, and first and second output object beam ports for the objectbeam and two output interference ports and includes means for dividingthe input beam along an object arm and a reference beam along areference arm each starting at the respective first output and secondoutput of a first optical splitter; light from the first output of thefirst optical splitter is sent to a first input port of a second opticalsplitter and the light at one of the corresponding output port of thesecond optical splitter is sent towards the said first output objectbeam port of the interferometer and the port of the second opticalsplitter where light traveling from the said first output object beamport of the core interferometer originates from is optically connectedto the first input of a confocal optical splitter and the first outputof the confocal optical splitter is optically connected to the firstinput of a third optical splitter and where the second output of theconfocal optical splitter sends light towards the said second outputobject beam port of the core interferometer and the second input of thethird optical splitter receives light from the second output of thefirst optical splitter via a delay line and where the outputs of thethird optical splitter provide signals to the two said outputinterference ports of the core interferometer; the reference path isdefined as the path taken by the reference beam from the first opticalsplitter via the delay line up to the third splitter; the object path isdefined as the path taken by the object beam from the first splitter,via the second splitter, a focusing element, said scanner means, andinterface optics to a depth inside the object to be investigated andtherefrom back via the interface optics, scanner, focusing elementtowards the second splitter, confocal optical splitter up to the thirdsplitter; the delay line is adjusted to match the optical length of thereference path to the length of the object path; and a polarizationcontroller is provided to match the orientation of the polarization inthe object and reference paths.
 33. The optical coherence tomographyapparatus of claim 32, wherein said focusing means are synchronouslyadjusted with the movement of the translation stage to maintain in thefocus the point where the optical path length of the reference path ismatched to the path length of the object path.
 34. The optical coherencetomography apparatus of claim 1, wherein: said interferometer comprisesmeans for dividing the input beam along an object arm and a referencebeam along a reference arm starting at the respective first output andsecond output of a second optical splitter; light from the first outputof the second optical splitter is sent to the said first output objectbeam port for the object beam of the core interferometer and the secondoutput of the second optical splitter is optically connected via a delayline to the first input of a third optical splitter whose outputs sendslight towards the said two output interference ports of the coreinterferometer and where the second input of the second optical splitteris optically connected to the first input of a confocal optical splitterand the first output of the confocal optical receiver is opticallyconnected to the second input of the third optical splitter and thesecond output of the confocal optical splitter is connected to the saidsecond object beam port for the object beam of the core interferometer;the reference path is defined as the path taken by the reference beamfrom the second optical splitter via the delay line up to the thirdoptical splitter; the object path is defined as the path taken by theobject beam from the second splitter, via the focusing element,transverse scanning means, interface optics up to a depth inside theobject to be investigated and therefrom back via the interface optics,transverse scanning means, focusing element towards the second opticalsplitter, confocal optical splitter and then up to the third opticalsplitter; the delay line is adjusted to match the optical length of thereference path to the length of the object path; and a polarizationcontroller is provided to match the orientation of the polarization inthe object and reference paths.
 35. The optical coherence tomographyapparatus of claim 34, wherein said focusing means are synchronouslyadjusted with the movement of the translation stage to maintain in thefocus the point where the optical path length of the reference path ismatched to the path length of the object path.
 36. The optical coherencetomography apparatus of claim 1, wherein the optical radiation source isless than 1 mm.
 37. The optical coherence tomography apparatus of claim1, wherein said scanner comprises a transverse scanning means split intoa line scanner and a frame scanner which are interleaved with elementsof interface optics for independent control of curvature of the scannedsurface along rectangular directions to the optic axis.